Toothbrushes are well known articles generally comprising a head for insertion in the user's mouth and a grip handle to be held during use, with a neck region in between. The toothbrush head normally has a surface, termed herein the “bristle surface” from which bristles extend from a lower end of the bristles closest to the bristle surface to an upper end distant from the bristle surface. Toothbrush bristles are also well known articles, generally comprising a filament of a stiff but flexible material, disposed in tufts of plural filaments extending from the bristle surface. The polyamide Nylon is very frequently used as a toothbrush bristle material.
Although in most toothbrushes the bristle filaments have the same cross-section along their entire length from their lower to their upper end except for the extreme upper end which is end-rounded, it is also known to use tapered bristles which decrease in their cross section toward their upper end in a shallow generally conical sloping profile. Tapered bristles, being thinner at their upper end, have different bending and flexibility characteristics to non-tapered filaments. In particular tapered bristles are known for efficacy in reaching into the spaces between the teeth, the so called “interproximal” spaces. For example such bristles are disclosed in EP-A-1 234 525, EP-A-1 415 572, U.S. Pat. No. 6,546,586, WO-A-97/42853, WO-A-97/42854, WO-A-01/32053, WO-A-01/82741, EP-A-0 596 633 among others.
Particular relative dispositions of the tapered bristles on the bristle surface are also known. For example U.S. Pat. No. 6,546,586 discloses a toothbrush head in which each tuft comprises plural bristle filaments made of polybutylene terephthalate in the form of shorter filaments of uniform cross section and longer filaments which taper toward their upper end. It is known to combine tapering and non-tapering bristles on a toothbrush head, e.g. from US-A-2006/0096053 which discloses a head for an electric toothbrush. It is also known from other disclosures to combine long and short bristle filaments in a tuft e.g. U.S. Pat. No. 3,103,679, WO-A-96/16571 and DE-A-35 28 596.
Generally there are two methods of producing such tapered bristles. One method is to chemically erode the ends of the bristle filaments. The other is to mechanically abrade them to a taper. It has previously been found difficult to accurately mechanically abrade bristle filaments in situ on a toothbrush head, particularly to achieve differences in length between tapered and non-tapered bristles. A known toothbrush of the type disclosed in WO-A-96/16571 is known to have been unsuccessful commercially because of poor mouth feel. However recent new mechanical bristle abrasion technologies have opened up new possibilities for exploring variations in length, inclination, tufting patterns etc. of tapered toothbrush bristles, especially in combination with non-tapered bristles.
It is an object of this invention to explore the possibilities of toothbrush heads with combinations of tapered and non-tapering bristles, especially with the intention of providing an improved toothbrush head incorporating tapered bristle filaments, e.g. providing tooth cleaning, particularly in the interproximal spaces, at the gingival margin, in subgingival access, and also having manufacturing advantages. Other objects and advantages of the invention will be apparent from the following description.